Isolation and structure determination of a new lasso peptide subterisin from Sphingomonas subterranea

Lasso peptides realm: Insights and applications

Lasso peptides exhibit a range of bioactivities, including antiviral effects, inhibition of the glucagon receptor, blockade of the endothelin type B receptor, inhibition of myosin light chain kinase, and modulation of the atrial natriuretic factor, as well as notable antimicrobial properties. Intriguingly, lasso peptides exhibit remarkable proteolytic and thermal stability, addressing one of the key challenges that traditional peptides often face. The challenge in producing those valuable peptides remains the main hurdle in the way of producing larger quantities or even modifying them with more potent analogues. Genome mining and heterologous expression approaches have greatly facilitated the production of lasso peptides, moving beyond mere isolation techniques. This advancement not only allows for larger quantities but also enables the creation of additional analogues with improved stability and potency. This review aims to explore the unique bioactivities and stability of lasso peptides, along with recent advancements in genome mining and heterologous expression that address production challenges and open pathways for engineering potent analogues.

Advances in lasso peptide discovery, biosynthesis, and function

Lasso peptides are a large and sequence-diverse class of ribosomally synthesized and post-translationally modified peptide (RiPP) natural products characterized by their slip knot-like shape. These unique, highly stable peptides are produced by bacteria for various purposes. Their stability and sequence diversity make them a potentially useful scaffold for biomedically relevant folded peptides. However, many questions remain about lasso peptide biosynthesis, ecological function, and diversification potential for biomedical and agricultural applications. This review discusses new insights and open questions about lasso peptide biosynthesis and biological function. The role that genome mining has played in the development of new methodologies for discovering and diversifying lasso peptides is also discussed.

Utilization of lasso peptides for biodegradation of polycyclic aromatic hydrocarbons

Many microbial genes involved in degrading recalcitrant environmental contaminants such as polycyclic aromatic hydrocarbons (PAHs) have been identified and characterized. However, all molecular mechanisms required for PAH utilization have not yet been elucidated. In this work, we demonstrate the proposed involvement of lasso peptides in the utilization of the PAH phenanthrene in Sphingomonas BPH. Transpositional mutagenesis of Sphingomonas BPH with the miniTn5 transposon yielded 3 phenanthrene utilization deficient mutants, #257, #1778, and #1782. In mutant #1782, Tn5 had inserted into the large subunit of the naph/bph dioxygenase gene. In mutant #1778, Tn5 had inserted into the B2 protease gene of a lasso peptide cluster. This finding is the first report on the role of lasso peptides in PAH utilization. Our studies also demonstrate that interruption of the lasso peptide cluster resulted in a significant increase in the amount of biosurfactant produced in the presence of glucose when compared to the wild-type strain. Collectively, these results suggest that the mechanisms Sphingomonas BPH utilizes to degrade phenanthrene are far more complex than previously understood and that the #1778 mutant may be a good candidate for bioremediation when glucose is applied as an amendment due to its higher biosurfactant production.

Peptidase Activation by a Leader Peptide-Bound RiPP Recognition Element

The RiPP precursor recognition element (RRE) is a conserved domain found in many prokaryotic ribosomally synthesized and post-translationally modified peptide (RiPP) biosynthetic gene clusters (BGCs). RREs bind with high specificity and affinity to a recognition sequence within the N-terminal leader region of RiPP precursor peptides. Lasso peptide biosynthesis involves an RRE-dependent leader peptidase, which is discretely encoded or fused to the RRE as a di-domain protein. Here we leveraged thousands of predicted BGCs to define the RRE:leader peptidase interaction through evolutionary covariance analysis. Each interacting domain contributes a three-stranded β-sheet to form a hydrophobic β-sandwich-like interface. The bioinformatics-guided predictions were experimentally confirmed using proteins from discrete and fused lasso peptide BGC architectures. Support for the domain-domain interface derived from chemical shift perturbation, paramagnetic relaxation enhancement experiments, and rapid variant activity screening using cell-free biosynthesis. Further validation of selected variants was performed with purified proteins. We developed a p-nitroanilide-based leader peptidase assay to illuminate the role of RRE domains. Our data show that RRE domains play a dual function. RRE domains deliver the precursor peptide to the leader peptidase, and the rate is saturable as expected for a substrate. RRE domains also partially compose the elusive S2 proteolytic pocket that binds the penultimate threonine of lasso leader peptides. Because the RRE domain is required to form the active site, leader peptidase activity is greatly diminished when the RRE domain is supplied at substoichiometric levels. Full proteolytic activation requires RRE engagement with the recognition sequence-containing portion of the leader peptide. Together, our observations define a new mechanism for protease activity regulation.

Unusual Post-Translational Modifications in the Biosynthesis of Lasso Peptides

Lasso peptides are a subclass of ribosomally synthesized and post-translationally modified peptides (RiPPs) and feature the threaded, lariat knot-like topology. The basic post-translational modifications (PTMs) of lasso peptide contain two steps, including the leader peptide removal of the ribosome-derived linear precursor peptide by an ATP-dependent cysteine protease, and the macrolactam cyclization by an ATP-dependent macrolactam synthetase. Recently, advanced bioinformatic tools combined with genome mining have paved the way to uncover a rapidly growing number of lasso peptides as well as a series of PTMs other than the general class-defining processes. Despite abundant reviews focusing on lasso peptide discoveries, structures, properties, and physiological functionalities, few summaries concerned their unique PTMs. In this review, we summarized all the unique PTMs of lasso peptides uncovered to date, shedding light on the related investigations in the future.

How to harness biosynthetic gene clusters of lasso peptides

Lasso peptides produced by bacteria have a very unique cyclic structure (“lasso” structure) and are resistant to protease. To date, a number of lasso peptides have been isolated from proteobacteria and actinobacteria. Many lasso peptides exhibit various biological activities, such as antibacterial activity, and are expected to have various applications. Based on study of genome mining, large numbers of biosynthetic gene cluster of lasso peptides are revealed to distribute over genomes of proteobacteria and actinobacteria. However, the biosynthetic gene clusters are cryptic in most cases. Therefore, the combination of genome mining and heterologous production is efficient method for the production of lasso peptides. To utilize lasso peptide as fine chemical, there have been several attempts to add new function to lasso peptide by genetic engineering. Currently, a more efficient lasso peptide production system is being developed to harness cryptic biosynthetic gene clusters of lasso peptide. In this review, the overview of lasso peptide study is discussed.

Heterologous production of new lasso peptide koreensin based on genome mining

Lasso peptides are a class of ribosomally biosynthesized and posttranslationally modified peptides with a knot structure as a common motif. Based on a genome search, a new biosynthetic gene cluster of lasso peptide was found in the genome of the proteobacterium Sphingomonas koreensis. Interestingly, the amino acid sequence of the precursor peptide gene includes two cell adhesion motif sequences (KGD and DGR). Heterologous production of the new lasso peptide was performed using the cryptic biosynthetic gene cluster of S. koreensis. As a result, a new lasso peptide named koreensin was produced by the gene expression system in the host strain Sphingomonas subterranea. The structure of koreensin was determined by NMR and ESI-MS analysis. The three-dimensional structure of koreensin was obtained based on an NOE experiment and the coupling constants. A variant peptide (koreensin-RGD), which had RGD instead of KGD, was produced by heterologous production with site-directed mutagenesis experiment. Koreensin and koreensin-RGD did not show cell adhesion inhibitory activity, although the molecules possessed cell adhesion motifs. The possible presence of a salt bridge between the motifs in koreensin was indicated, and it may prevent the cell adhesion motif from functioning.

Phylogenetic distribution of the bacteriocin repertoire of lactic acid bacteria species associated with artisanal cheese

The microbiota contributes to artisanal cheese bioprotection and biopreservation through inter and intraspecific competition. This work aimed to investigate the phylogenetic distribution of the repertoire of bacteriocin structural genes of model lactic acid bacteria (LAB) in order to investigate its respective role in the artisanal cheeses microenvironment. A phylogenetic analysis of the rRNA 16S gene from 445 model strains of LAB was conducted using bayesian inference and the repertoire of bacteriocin genes was predicted from these strains by BAGEL software. Bacterial strains were clustered in five monophyletic clades (A, B, C, D and E) with high posterior probability values (PP > 0.99). One bacteriocin structural gene was predicted for 88.5% of the analyzed strains. The majority of the species encoded different classes of bacteriocins. Greater diversity of bacteriocin genes was found for strains included in clade A, comprising Lactococcus lactis, Streptococcus agalactiae, Streptococcus thermophilus, Streptococcus macedonicus, Enterococcus faecalis and Enterococcus faecium. In addition, Lactococcus lactis presented higher diversity of bacteriocin classes, encoding glycocins, lanthipeptides, sactipeptides, cyclic and linear azole-containing peptides, included in bacteriocins class I, besides class II and III. The results suggest that the distribution of bacteriocin structural genes is related to the phylogenetic clades of LAB species, with a higher frequency in some specific clades. Information comprised in this study contributes to comprehend the bacterial competition mechanisms in the artisanal cheese microenvironment.

Genome mining for lasso peptides: past, present, and future

Over the course of roughly a decade, the lasso peptide field has been transformed. Whereas new compounds were discovered infrequently via activity-driven approaches, now, the vast majority of lasso peptide discovery is driven by genome-mining approaches. This paper starts with a historical overview of the first genome-mining approaches for lasso peptide discovery, and then covers new tools that have emerged. Several examples of novel lasso peptides that have been discovered via genome mining are presented as are examples of new enzymes found associated with lasso peptide gene clusters. Finally, this paper concludes with future directions and unsolved challenges in lasso peptide genome mining.

General lack of structural characterization of chemically synthesized long peptides

Many peptide chemistry scientists have been reporting extremely interesting work on the basis of chemical peptides for which the only characterization was their purity, mass, and biological activity. It seems slightly overenthusiastic, as many of these structures should be thoroughly characterized first to demonstrate the uniqueness of the structure, as opposed to the uniqueness of the sequence. Among the peptides of identical sequences in the final chemical preparation, what amount of well-folded peptide supports the measured activity? The activity of a peptide preparation cannot prove the purity of the desired peptide. Therefore, greater care should be taken in characterizing peptides, particularly those coming from chemical synthesis. At a time when the pharmaceutical industry is changing its paradigm by moving substantially from small molecules to biologics to better serve patients' needs, it is important to understand the limitations of the descriptions of these products and to start to apply the same "good laboratory practices" to our peptide research. Here, we attempt to delineate how synthetic peptides are described and characterized and what will be needed to describe them in regards to how they are well-folded and homogeneous in their tertiary structure. Older studies were done when the tools were not yet discovered, but more recent publications are still lacking proper descriptions of these peptides. Modern tools of analysis are capable of segregating folded and unfolded peptides, even if the preparation is biologically active.

Heterologous production of a new lasso peptide brevunsin in Sphingomonas subterranea

A shuttle vector pHSG396Sp was constructed to perform gene expression using Sphingomonas subterranea as a host. A new lasso peptide biosynthetic gene cluster, derived from Brevundimonas diminuta, was amplified by PCR and integrated to afford a expression vector pHSG396Sp-12697L. The new lasso peptide brevunsin was successfully produced by S. subterranea, harboring the expression vector, with a high production yield (10.2 mg from 1 L culture). The chemical structure of brevunsin was established by NMR and MS/MS experiments. Based on the information obtained from the NOE experiment, the three-dimensional structure of brevunsin was determined, which indicated that brevunsin possessed a typical lasso structure. This expression vector system provides a new heterologous production method for unexplored lasso peptides that are encoded by bacterial genomes.